The present application claims priority under 35 U.S.C. xc2xa7119 based upon Japan Patent Application No. JP2001-254920, filed on Aug. 24, 2001.
The present invention relates to a pressure sensor for measuring the pressure of a fluid, and particularly relates to a pressure sensor preferably used for measuring the pressure of a corrosive solution, organic solvent, pure water and another liquids, and gases which are used for wet treatments of semiconductors.
Conventionally, in the manufacture of semiconductors such as in very large-scale integration, a large number of wet treatments are performed in processes such as washing and etching of surfaces of wafers and the like. In these treatments, corrosive solutions, organic solvents, and pure water and other liquids such as IPA have purity or detergency higher than those which are used for the treatment of ordinary semiconductors. In addition, some gases are sometimes used for in treatments.
In order to measure the pressure of such fluids, a pressure sensor 20 as shown in FIG. 3 is connected with a tube 22 in which the fluid flows therein by a joint 21. The pressure sensor 20 is, as shown in FIG. 4, composed of a duct 23 in which the fluid from the tube 22 is drawn therein, a sensor element 24 which is provided on the end portion of the duct 23, and a housing 25 which holds the sensor element. A pressure measuring portion 26 which receives pressure of the fluid is provided on the surface of the sensor element 24 which opposes the duct 23. Furthermore, an outside of the sensor element 24 is covered by a cap 28, and the sensor element 24 is held in the housing 25 so as to contact with the pressure measuring portion 26 by the cap 28.
When the fluid is a corrosive solution, the housing 25 and pressure measuring portion 26 are mainly made of a fluororesin which has a high chemical resistance, and when the fluid is pure water or IPA, the housing 25 is mainly made of metal.
The sensor element 24 has a circuit for converting the stress toward the pressure measuring portion 26 into electrical signals. This circuit includes a Wheatstone bridge circuit composed of four resistors R1-R4 as shown in FIG. 5, and an output voltage Vout is changed to comply with the change of resistors R1-R4. When no pressure is applied on the sensor element 24, this output voltage Vout is zero; however, when pressure is applied on the sensor element 24 and resistance of the resistors R1-R4 changes, the output voltage Vout also changes, and this value of the output voltage Vout is converted to the pressure value of the fluid.
As shown in FIG. 6, in these resistors R1-R4, the resistors R2 and R4 are provided at a central portion of the sensor element 24, and the resistors R1 and R3 are provided at edge portions of the sensor element 24. When pressure is applied to the sensor element 24 from the fluid through the pressure measuring portion 26, the resistors R2 and R4 which are provided at the central portion of the sensor element 24 are extended and their resistances increase, and the resistors R1 and R3 which are provided at the edge portions of the sensor element 24 are pressed from both sides and their resistances decrease. As a result, the output voltage Vout also changes to comply with the change of the pressure on the sensor element 24, and the pressure of the fluid which flows in the tube 22 can be measured from the value of the output voltage Vout.
When the housing 25 is made of a resin which has high chemical resistance, since the resin is easily electrified, friction occurs between the inner surface of the tube 22 and the fluid which flows in the tube 22, and static electricity generated by this friction is accumulated in the part in the vicinity of the duct 23 of the housing 25 and the pressure measuring portion 26. The static electricity accumulated in the pressure measuring portion 26 is discharged to the sensor element 24 in proportion to the operating time of the pressure sensor 20. As a result, noise is caused in circuits in the sensor element 24 or the circuit is damaged by electrical discharge, and a measurement of the pressure is inadequately performed or cannot be performed. When the housing 25 is made of metal, although the static electricity does not accumulate in the housing 25, the static electricity still accumulates in the pressure measuring portion 26 and is discharged to the sensor element 24.
To solve this problem, the structure having a lead wire 29 which connects the cap 28 and a ground is proposed. According to this structure, the static electricity can be released from the pressure measuring portion 26 through the lead wire 29 when a fluid such as the high purity corrosive solution or pure water, or gases, flows in the tube 22.
However, when the housing 25 is made of a resin which is easily electrified and a fluid which easily generates static electricity such as IPA or other alcohol, or gases, flows in the tube 22, since static electricity which is higher than the normal level is generated, the static electricity cannot be entirely released through the lead wire 29 since the lead wire 29 is not directly connect with the pressure measuring portion 26. As a result, the possibility of the discharge of the static electricity still remains.
The present invention is prepared in consideration of the above circumstances, and a purpose of the present invention is to provide a pressure sensor which has high chemical resistance and high discharge capacity of static electricity.
In order to achieve the above purpose, the pressure sensor of the first aspect of the present invention comprises a pressure measuring portion which is composed of a resin and contacts fluid, and a sensor element which measures pressure imposed on the pressure measuring portion; wherein a conductive layer which is composed of a foil having electric conductivity is provided between the pressure measuring portion and sensor element, and the conductive layer is connected to a ground.
The pressure sensor of the second aspect of the present invention comprises a pressure measuring portion which is composed of a resin and contacts fluid, and a sensor element which measures pressure imposed on the pressure measuring portion; wherein a conductive layer which is composed of meshes having electric conductivity is provided between the pressure measuring portion and sensor element, and the conductive layer is connected to a ground.
According to the pressure sensors having the above structures, the static electricity accumulated in the pressure measuring portion is released from the pressure measuring portion through the conductive layer. Therefore, discharge of the static electricity accumulated in the pressure measuring portion to the sensor element and harmful effect caused by this discharge are prevented.
In the pressure sensors having the above structures, it is preferable that the sensor element be held in a housing of the pressure sensor via a cap which is composed of a material having electric conductivity and is connected to a ground, and that the conductive layer contact the cap.
According to the pressure sensor having the above structure, the sensor element is reliably held in the housing via the cap. Furthermore, the conductive layer provided between the pressure measuring portion and sensor element is easily connected to a ground by contacting the conductive layer with the cap and connecting the cap to a ground. Therefore, the manufacturing and assembly of the pressure sensor are simplified.